Re: Your wish list for Ada 202X

[Peter Chapin <PChapin@vtc.vsc.edu>]

On 2014-03-30 10:28, Simon Clubley wrote:

> Also, I'm not quite sure what you mean by the latter. As far as I can see,
> the parameter passing would be left to right, just as it is in C.

Typical C compilers push arguments onto the stack from right to left.
This is done to support variable length parameter lists such as what
printf() has. For example

    printf("%d\n", some_integer);

The printf function expects to find a pointer to the format string on
the top of the stack. It reads that string to find out what other
arguments to expect and then it indexes down the stack to get them. If
the compiler pushed arguments from left to right the critical pointer to
the format string would be beneath an unknown number of other arguments.

Standard C requires that functions with variable length parameter lists
be prototyped (this is a break from pre-standard C). This gives compiler
writers the option of using a different calling convention by default
and something special for functions with variable length parameters,
since the compiler can be sure such functions will be prototyped and
thus known to the compiler. Some compilers do take advantage of this and
will incorrectly compile calls to printf() if one does not #include
<stdio.h> or otherwise provide a prototype for printf().

Peter